Gamma-acetyl pimelic acid and diesters thereof



tures much below 60 Patented Apr. 6, 1948 GAMMA-ACETYL PIMELIC ACID AND DIESTERS THEREOF Albert B. Boese, Jr.,

Pittsburgh, Pa., assignmto Carbide and Carbon Chemicals Corporation, a

corporation oi New York No Drawing. Application May 29, 1945, Serial No. 596,587

This invention relates to diesters of Y-acetyl pimelic acid, and to a novel method for producing such esters from adducts of acrylonitrile and diketone's. rendering them useful as resins and other resinous plastics, cellulose esters and ethers, and other materials. One feature of the invention concerns the production of 3,3'-dicyan0ethyl alkanediones-2,4, which are valuable intermediate compounds useful in the production of esters of Y-acetyl pimelic acid. The invention has especial utility for the production of the higher dialkyl, diaryl, dialkoxyalkyl and diaryloxyalkyl esters of y-acetyl pimelic acid from adducts of acrylonitrile and pentanedione- 2,4.

According to this invention, a 2,4-diketone having a reactive methylene group connecting the carbon atoms of the respective keto groups is condensed with acrylonitrile, in the presence of a basic condensation catalyst. Under such conditions 2 mols of the acrylonitrile condense with 1 mol of the diketone to form a 3,3'-dicyanoethyl dime-2,4. The reaction mixture is then cooled and the resultant dicyanoethyl dione present therein is separated as a crystalline solid by filplasticizers for vinyl tration. It may then be Washed with water, or

otherwise purified.

The condensation reaction may be carried out by adding the catalyst to a stoichiometric mixture of the reactants but, under these conditions, the exothermic nature of the reaction makes the control thereof somewhat difficult. More satisfactory results are secured by introducing a mixture of the reactants into a liquid diluent containing the catalyst, which diluent preferably is substantially inert to acrylonitrile. Secondary alcohols such as isopropanol, and tertiary alcohols such as tertiary butanol, are eminently suitable as diluents; although other inert diluents such as the aromatic hydrocarbons; the aliphatic ethers such as diethyl ether and dioxane; and chlorinated solvents such as chlorinated hydrocarbons and ethers may be effectively employed.

The acrylonitrile also may be added to a solution of the diketone in the diluent containing the catalyst. However, better yields are generally obtained by adding a stoichiometric mixture of the reactants to the diluent containing the catyst.

The condensation reaction is preferably conducted at a temperature between around 60 C. and around 100 C., although higher and lower temperatures may be employed. At tempera- C. the condensation reac- Many of these esters have properties 7 Claims. 260-483) trile may be built up before the condensation is i the corresponding dicyanoethyl diones.

initiated. V

Among 2,4-diketones suitable for use in the process may be mentioned acetyl acetone (pen,-

tanedione-2,4), propionyl acetone, acetyl isobutyryl methane, acetyl caproyl methane, propionyl acetophenone, benzoyl acetone, etc. Acryloni trile reacts with these higher diketones to yield However, the higher diones thus produced have no advantage over the more readily available pentanedione derivatives as intermediates for the production of diesters of 4-acety1 pimelic acid.

The most effective catalysts used in the condensation are strongly basic materials, the more active ones being the alkali metal hydroxides such as sodium and potassium hydroxides, and quaternary organic bases such as trimethyl benzyl ammonium hydroxide and tetraethanolammonium hydroxide. The catalyst usually is em played in the form of a 40% to 50% aqueous solution.

The condensation reaction may be represented by the following equation:

wherein R represents either an alkyl or an aryl group containing from 1 to 12 carbon atoms. The resultant product may be defined as a Y-dia-cyl pimelonitrile wherein at least one acyl. group is the acetyl group.

The 3,3-dicyan0ethyl dione-2,4 formed in the aforesaid condensation does not, upon hydrolysis with mineral acids or with alkali metal hydroxides, yield the expected diacyl pimelic acids, but, instead, yields Y-acetyl pimelic acid. During the hydrolysis one acyl group is split ,off to form the corresponding carboxylic acid. Thus, the hydrolysis of 3,3'-dicyanoethyl pentanedione- 2,4 splits off one acetyl group as acetic acid.

The y-acetyl pimelic acid formed. is a watersoluble, non-crystalline compound whose isolation from the hydrolysis reaction mixture requires repeated and tedious extractions .with a solvent such as diethyl ether.

According to a preferred form of the present invention, the 3,3'-dicyanoethyl alkanedione-2,4 is directly converted to a dialkyl, diaryl, dialkoxyalkyl or diaryloxyalkyl ester of Y-acetyl pimelic acid by a simultaneous hydrolysis and esterification which has proven to be highly emcient. This result is readily accomplished by heating the 3.3'-dicyanoethyl alkanedione -2,4 in the presence 01' an hydrolysis and esteriflcation catalyst such as sulfuric acid, with a monohydric aliphatic or aromatic alcohol. a monoalkyl or cohols such as methanol, butanol, hexanol, 2-

ethylhexanol, decanol, and the higher alcohols; aromatic alcohols such as benzyl alcohol; the monoalkyl and monoaryl ethers of glycols such as the monoethyl and monophenyl ethers of ethylene glycol andoi diethylene glycol; and glycerol dimethyl ether.

Esterifying agents that provide esters havin alkyl groups or aryl groups containing at least 6 carbon atoms, or having alkoxyalkyl or aryloxyalkyl groups containing at least 3 carbonatoms, are preferred, since the resultant 4-acetyl pimelic acid diesters appear to possess valuable properties adapting them for use as plasticizers for thermoplastic resinous materials such as the various vinyl resins.

The concurrent hydrolysis and esterification reactions preferably are conducted at temperatures ranging from about 60 C. to about 150 C. When treating a dicyanoethyl alkaned-ione- 2,4, during the reaction one acyl group of the dicyanoethyl alkanedione ered in the form of an ester of a fatty acid. The reaction involved may be generally represented by the following equation:

(CHaCO) (RCO) C (CHzCHzCN) 2+2H20+ 3R'OH-I-H2SO4 CH3COCH (CI-IzCHaCOOR' 2+ RCOOR (NH4) 2304 'R is a radical selected from the class consisting of the alkyl radicals, the aryl radicals, the al- -koxyalkyl radicals, and the aryloxyalkyl radicals.

By subjecting the aforesaid dicyanoethyl dimes-2,4 concurrently to hydrolysis and esterification reactions in the presence of aliphatic alcohols and alcohol ethers, it is possible to produce directly from the dicyanoethyl diones, in simple manner and in good yields, the diesters of Y- acetyl pimel ic acid with even the. higher alkyl alcohols and alcohol ethers such as hexanol, 2- ethylhexanol, the decanols, the tetradecanols, and the monoethyl and monobutyl ethers of ethylene glycol and of the polyethylene glycols.

It will be understood that the Y-acetyl pimelic acid esters of the higher alcohols and alcohol ethers canalso be produced somewhat less conveniently by an ester exchange reaction between such alcohol or alcohol ether and the dimethyl or diethyl ester of 'y-acetyl pimelic acid, catalyzedwith an acid such as sulfuric acid.

The following examples serve to illustrate the invention:

Example l.3,3'-di(cyanoethyl)- pentlmedionegrams (2 mols) of acrylonitrile were introduced in successive portions into 400 cc. of refluxing isopropanol containing 1 cc. of a 50% aqueous solution of potassium hydroxide. During this period an additional 9 cc. of catalyst were added at equalis split ,off and recov- I ly spaced intervals. After refluxing for an addicured in the form of colorless crystals melting at 182' C.-184 C.

10 Example I l. 3,3-di(cyanoethyl) i acetone 3 '-benzoyl During two hours a solution of 75 grams (0.46 mol) of benzoyl acetone and 49 grams (0.92 mol) of acrylonitrile in 200 cc. of isopropanol were added slowly with stirring to a refluxing solu-' tion of 200 cc. of isopropanol containing 2 cc. of

a 50% aqueous potassium hydroxide solution. During this period an additional 3 cc. of the potassium hydroxide solution were added, and refluxing. was continued for an additional two hours. The isopropanol was then distilled off, 200 cc. of water were added to the residue, the mixture was extracted with benzene, and the benzene extract washed with water. Upon frac- 'tional distillation of the washed extract under subatmospheric pressure after removal of the benzene, there was secured a yield of 65% of dicyanoethyl benzoyl acetone, in the form of a pale yellow oil boiling at from 175 C. to 178 C.

under an absolute pressure of 2.5 mm. of mercury. It had a specific gravity of 1.1128 a1 20/20 C. and a refractive index, 20/D of 1.5365

Example III.Y-acetyl di(z-ethylhemyl) pimelate A mixture of 25 grams of 3,3'-di(cyanoethyl) pentaned-ione-2,4, 100 grams of 2-ethylhexanole 1, and 29 grams of an 83% aqueous solution of sulfuric acid were heated for eighteen hours at 40 130 C.-140 C. in an open vessel. The resultant dark red liquid was washed with waterto remove sulfuric acid and ammonium sulfate, and was fractionally distilled undersubatmospheric pressure. After removal of the excess 2-ethylhexanol and the 2-ethylhexyl acetate which had been formed, 'Y-acetyl di-(2-ethylhexyl) pimelate was obtained in a yield of over 87%, based upon the dicyanoethyl pentanedione employed; This novel compound .is a. pale, straw-colored liquid boiling between 235? C. and 240 C. under an absolute pressure of 4 mm. of mercury. It has a specific gravity of 0.9656 at 20/4 C.; and a refractive index at 20 C. of 1.4555.

Example IV.'y-acetyldi-(butoxyethyl) pimelate A mixture of 100 grams of butoxyethanol, 25 grams of concentrated sulfuric acid and 25 grams of 3,3'-dicyanoethy1 pentanedione-2,4 was heated on a steam bath for forty hours. The resultant darkred solution was washed with water to remove sulfuric acid and, ammonium sulfate.

The washed solution was fractionally distilled under vacuum, and the Y-acetyl di-(bu'toxyethyl) pimelate was recovered in a yield around 77%,

after removal andrecovery of unreacted butoxyethanol and some butoxyethyl acetate.

The Y-acetyl di(butoxyethyl) pimelate, or di- (fi-butoxyethyl) ester of Y-acetyl pimelic acid,

is a pale yellow liquid boiling at from 205 C.

to 215 C. under an absolute pressure of between 1.5 and 2 mm. of mercury. It has a specific gravity at 20/4 C. of 1.0237; and has a refractive index at 20 C. of 1.4547.

By substituting for the glycol ether recited in Example IV the monophenyl ether of ethylene glycol, the di-phenoxyethyl ester of Y-acetyl plmelic acid may be produced; while by substituting the monobutyl ether of diethylene glycol, the di-(,B-butoxy-fi'ethoxyethyl) ester of Y-acetyl pimelic acid may be produced.

Example V.y-acetyl diethyl pz'melate A mixture of 100 cc. of 90% ethanol, 50 cc. of concentrated sulfuric acid, and 33 grams of 3,3'-dicyanoethyl pentanedione-2,4 was refluxed for forty hours under a refluxing head, during which time approximately 1 mol of ethyl aceate was removed by distillation, and ammonium sulfate was formed. The residual mixture then was added to 700 cc. of water, and the oily layer which separated was extracted with ether, and the extract dried over sodium sulfate. After removal of the ether, Y-acetyl diethyl pimelate was obtained in amount corresponding to a yield of 83.3%, based upon the dicyanoethyl pentanedione starting material.

The terms alcohol alcoholic esteriiying agent" and similar expressions are used in the claims to designate not only the monohydric aliphatic and aromatic alcohols but also the monoalkyl and monoaryl ethers of the alkylene glycols and of the diand polyalkylene glycols; and the dialkyl ethers of glycerol, such as glycerol dimethyl ether.

The invention is susceptible of modification within the scope of the appended claims.

I claim:

1. Process which comprises the step of hydrolyzing a Y-diacyl pimelonitrile wherein at least one acyl group is the acetyl group by heating such diacyl pimelonitrile in the presence of moisture and an hydrolysis catalyst, thereby splitting oil? one acyl group from said pimelonitrile and forming Y-acetyl plmelic acid.

2. Process for producing a diester of Y-acetyl plmelic acid, which comprises hydrolyzing a dicyanoethyl dione-2,4 by heating such dione at a temperature within the range between around 60 C. and around 150 C. in the presence of moisture, alcoholic esterifying agent and an asterification catalyst, thereby concurrently esterifyin the acid product of such hydrolysis, and recovering from the esterification reaction mixture the diester of l -acetyl pimelic acid thus produced.

3. Process for producing a diester oi Y-acetyl plmelic acid, which comprises hydrolyzing a dicyanoethyl dione-2,4 by heating such dione in the presence of moisture, an alcoholic esterifying agent and an acidic esterification catalyst, thereby concurrently esterlfying the acid product of the hydrolysis, and recovering from the esterification reaction mixture the diester of Y-acetyl pimelic'acid thus produced.

4. Process as defined in claim 3, wherein the 01. an ethylene glycol, and the resultant diester is a dialkoxyalkyl ester of Y-acetyl pimelic acid.

5. Process for producing a pimelic acid, which comprises hydrolyzing a ydiacyl pimelodinitrile wherein at least one acyl group is the acetyl radical by heating such dinitrile in the presence of moisture, an alcoholic esteril'ying agent and an acidic esterification catalyst, thereby concurrently esterifying the acid product of the hydrolysis, and recovering from the esterification reaction mixture the 'di ester of Y-acetyl pimelic acid thus produced.

6. Process for producing diesters of y-acetyl plmelic acid, which comprises hydrolyzing by heating at an elevated temperature, in the pres ence of moisture, an alcoholic esterifying agent,

and polyalkylene glycol and an acidic hydrolysis and esterification catalyst, a dicyanoethyl dione-2,4 having the structure CHaCO(RCO)C(CH2CH2CN)2 wherein R represents a group selected from the class consisting of the alkyl and aryl groups containing from 1 to 12 carbon atoms, thereby hydrolyzing said dione and simultaneously esterifying the hydrolyzed product as formed by means of an alcoholic esterifying agent, and recovering from the resultant reaction mixture the diester of lacetyl plmelic acid thus produced.

7. Process for producing diesters of Y-acetyl plmelic acid, which comprises hydrolyzing .a dicyanoethyl alkanedione-2,4 at a temperature within the range between around C. and around 150 C in the presence of moisture and an acidic hydrolysis and esterification catalyst, simultaneously esterifying the hydrolyzed product substantially as rapidly as formed by means of an alcoholic esterifying agent selected from the group consistingof the monohydric alcohols having at least 6 carbon atoms and the allgvlene monoalkyl ethers having at least 3 carbon atoms, and recovering from the resultant reaction acetyl plmelic acid thus produced.

, ALBERT B. BOESE, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 60 Number Name Date 2,374,327 Bruson Apr. 24, 1945 2,381,371 Shannon Aug. 7, 1945 2,383,444 Bruson Aug. 28, 1945 2,386,736 Bruson Oct. 9, 1945 OTHER REFERENCES Perkin et al.: Jour. Chem. Soc. (London), vol. 91 (1907). P ge 1741;

Ser. No. 877,664, Wiest (A. P. 0.), published alcoholic esterirying agent 13 a monoalkyl ether an April 20.

diester of Y-acetyl mixtures the diester of Y- 

